Diversity radio receiving system



Jan. 18, 1949. c, P,BEANLAND DIVERSITY RADIO RECEIVING SYSTEM Filed Dec. 7, 1944 INVENTOR. 17/04 157 FfiEHA/L FIND ITTbR/VEV Patented Jan. 18, 1949 DIVERSITY RADIO RECEIVING SYSTEM Charles Percy Beanland, Chelmsford, England, assignor to Radio Corporation of America, a corporation of Delaware Application December 7, 1944, Serial No. 567,014

In Great Britain October 25, 1943 Section 1, Public Law 690, August s, 1946 Patent expires October 25, 1963 4 Claims. 1

This invention relates to radio receivers and provides an improved receiver which can be used with but little modification either as an individual receiver, or as a constituent receiver in a diversity receiving system.

When it is desired to use, as constituent receivers of a diversity system, receivers which may also be used as individual receivers each having its own automatic gain controlling system, and to that end to arrange that the constituent receivers shall work into a common load, it is necessary to arrange that the automatic gain controllin system of the combined system shall respond to rapid changes in the intensities of potential arising from the received signal. This means that the automatic gain controlling system of the combined system must have a suitably small time-constant. The time constant of the automatic gain controlling system of each constituent receiver is, of course, largely determined by the electrical dimensions of the capacitor, and resistor in the decoupling circuit. It will be apparent that if the automatic gain controlling systems of a number of constituent receivers are merely connected together, the capacitors of the several decoupling circuits will, as a consequence, be connected in parallel so that the time constant will be so increased that the diversity receiving system, as a whole, does not respond to rapid changes of signal received by the constituent receivers.

The invention aims at overcomin the difficulty set out above arising from the employment of receivers adapted to be used individually, and

having their own automatic gain controlling system, as constituents of a diversity receiving system using the said automatic gain controlling systems to control the gain of the system as a whole.

As will be apparent, the time constant of the automatic gain controlling systems of receivers which is designed to give satisfactory performance when the receivers are operating individually, is modified for suitable and efiicient performance when the receivers are used as constituents of a diversity receiving system.

According to the invention, a diversity radio receivin system comprises a plurality of constituent receivers each of which embodies an automatic gain controlling system which ineludes an automatic gain load resistor to which the output of an automatic gain rectifier may be applied and from which automatic gain potentials are 1 derived forapplicatlon to amplifying stages of the receiver, in combinationrwith a unit common to all the constituent receivers which includes an input load resistor, to which the outputs from the automatic gain rectifier of said receivers are transferred from said automatic gain load resistors and applied in common, a valve to which potentials from across said input load resistor are applied, and an output load resistor for said valve, from which potentials are applied to the automatic gain load resistors of all the constituent receivers in common.

The said valve may be a diode-triode valve and may have its anode and cathode connected between the positive and negative terminals of a source of power, a resistor being included in the cathode lead between the said cathode and thenegative terminal of said source The said negative terminal may be at a potential which is lower than that of some suitable point on the said source of power which is at earth potential.

The said load resistors may have their one ends connected to a point at earth potential.

The automatic gain controlling system of this invention is so arranged that the individual receiver developing the highest automatic gain control voltage will control the gain of all'the constituent receivers in the diversity receiver system in such a manner that those receivers having a smaller input signal are rendered less sensitive. In this way, the signal-to-noise ratio of the complete diversity receiver is maintained at a satisfactory level in spite of rapid and substantial changes in voltage derived from signal received by the several receivers.

An arrangement for carrying the invention into effect is illustrated in the accompanying drawing. In the drawing, three receivers R], R2, and R3 are indicated, the former by an automatic gain diode I, time constant circuit 2, two terminals 3 and 4, and load resistor 5. Receiver R2 has terminals 6 and I, while receiver R3 has terminals 8 and 9. Receivers R2 and R3 are shown in block diagram since their circuits are similar in every respect to that of receiver RI. The anode la of automatic gain diode, such as I, in receiver RI, is disconnected from its normal connection to load resistor 5 and connected instead to a conveniently accessible terminal 3, on the receiver, say at the back thereof. The end of the load resistor 5, to which the said anode is normally connected, is also connected to a conveniently accessible terminal, such as t, .adja cent to terminal 3. Connection :5 and H go to the grid circuits of radio frequency and intermal connections are thereby established. When,

however, it is desired to use such a receiver as. a

constituent receiver of a diversity receiving-sysgtem, the two terminals .3 and 4 are disconnected 4 constituent receivers and thence, over leads l6 and I! to the controlled intermediate and high frequency valves respectively of these receivers. The automaticgain potential ior the intermediate frequency -"valves'f'of the-several constituent receivers is preferably taken from the top of the several automatic gain load resistors, as 5, whilst that for the high frequency valves is taken from a-point lower down -on these resistors.

If desired,-switches=. as l8, l9, and 20 may be 1 provided so that the automatic gain controlling -arrangementsofany of the receivers may be individualized. I

- 1 vI claim: Y n

from each other and terminal 3 ofthereceiverunder consideration is connected to a corresponding terminal 6 and 8 on other constituent receiveraas R2 and R3, and to one end of an input resistor 19' whose other end is connected to earth. It is to be' observed that the terminals ofthe'pair 6"; l", also'the'pair 8, 9' on these other receivers are also dlSCOI'lIIECtGd from each other; Oneerid' of resist'or"llf"is connected'to the grid 22 of a doublediode-triod'e valve H ,Since this resistor now-replaces the automatic gain resistors, similar to fi, of'a plurality of receivers, its resistive value must be'kept to the same order of magnitudeth'at is itmustloe'high. The anode l2 of the triode 'por tion of the double-diode tri'ode'valve"Ihis connested to the-positive terminal indicatedat -lz l UV of'a suitable source of high-tension energy; The cathode 2| is connected-through a resistor l- 3to a point-on s'aid source at a'su'itable negative' potential; indicated at l2EiV. The two anodes M of the diode portion'of the double diode-triode va'lve'are connected together and'to one 'end'of a potentiometer resistor 55. oflthis potentiometer resistor is small so" a's 'to provide a small time constant, since itis an" es sential; condition that the time constant ofthe combined automatic gain controlling-circuit be kept as low-as'ipossi'hle in orderthat the? receivers may quickly. respond to the fading of the signal as received byrthem-u connected together, thesum of the decoupling capacities of the several systems would provide a time constant which would be bigger than would lie-tolerable Terminals 4, 1, and 9 are the-terminals to which the automatic gain load resistors ineach receiver are individually connected. These. terminals may, however, be connected incommon to the slider on saidpotentiometer resistor l5 so that a controlled automatic gain-potentialmay be fed back to the automatic gain resistorasimilar-to 5 ofall the receivers in common.- 1

The system operates as follows: A negative potential will appear across input resistor Ill-due to signal picked upon any constituent'receiver. This potential applied to the grid22 of doublediode-triode valve l I. willdecrease the current therethrou'gh. The potential of the cathode 21 of the valve will consequently follow that of the grid, that is, it will go negative. The difierenc'e of potential between the anodes Hi, !4' and cathode 2| of the diode portion will thus increaseand the diode portions will consequently become conductive. The efiective potentials of the an odes [4," I4 of the diodes and of the upper end of the potentiometer resistor l5'wi1l become nega tive so that a negative potential will be fed ba'ck to the upper end of the automaticgain load resistors, such as 5, by way of the connection-from the top on resistor I5 to terminals 4,- .1, oi the It is apparent that if the automatic gain controlling-- circuits were merely The resistive'value.

control" circuit terminals to sai 1. A radio receiving system comprising a plurality of constituent receivers each including sign'aldtectir'i'g means and an automatic gain controlcircuit, each of said receivers having a terminal connected to said'adetecting means to receive the output thereof and a terminal connected to said automatic gain control circuit to fed'an automatic gain control voltage" thereto, a cornhining circuit having tam er and an} out; put, means for coupling all" of I said "te'ct "g means terminals to saitl'c'onibiningcircuit input and means foricouplirigall of saidautoniatic ain control circuit terminals'jto. said' combining cir:- cuit' output, said} combining circuit including a thermionicdischarge tubell'iavih g a plurality of cathodetoano'de discharge paths therein 'afnda' control electrode for infiueri cing'fthe catl'ioc'le to anode current in one of"saidipaths,saidf'coihhin ing circuit input being connected to saidfcontrol electrode j ft I V 2. A radio ,receiving'jsy'stem comprising a pin ralitylo'f constituent'receivers each includingi's naYd'etecting means and an automatic gain" trol' circuit, each ofsaidj receivers hayinga tel minal connectedto'said detectingv means tore:

ceive theoutputthereof and ajterininalfdon-y n'ectedtoi said automatic gain control il cult to: feed ana'utoma'tic' gain 'co'ntr'ol voltage thereto, a combining circuit havingan input andan" output, mean'sj 'for coupling' all" f of said detecting means terminals'tolsaidjcombi'ning circui' o and means for coupling 'allof, saidautomatijcfgairi m i er ir output,' said' combining circuit" including athe'r? m c d har ube av a P ur y 1 cathode" t'o" and tie discharge paths therein and a control electrode for influencing the catho'd'e' to anode current in" one of.s 'aid pathsifsaid com bining 'circuitinputbeing connected to said con"- trol "electrode," said; discharge path having "a 'fpor' 'f tion ofth'eir externalicircuits' in'co mon and said; combining "circuit output including airesistorjcon nectedfrom the anodegof the. other'of said tli-jj odeanode'p'aths to 'ground. t 1: 3 A radio receiving system comprisinga rality of constituent receivers each includ n signal detecting" means" and an automatic gain" controrcircuit, each o'f'isaid receivershaving' a terminal connected to said detecting "means to receive th'e'output thereof and a' terifiina l n'ected tosaid automaticgaincontrol circm-t -to feed an automatic gain"control voltag'ethereto; a combining circuithaving' an input arisen output,* meansforcoupling-"all of said d'etecting' means Y terminals tosaid combining circuit'input and means fdi cfi-lllplifilg all of'saidElifiOHifitifi control circuit terminals 2 to said combiriing. cuit? output," said combining circuit 'includm thermionic; discharge 'tube having: a plura I ofi cathode-toanode discharge patns herein an Y a control e1ectrode'ifor 'influencingthe "cathode-to anode current in one of said paths, said combining circuit input being connected to said control electrode, said discharge paths having a portion of their external circuits in common and said combining circuit output including a resistor connected from the anode of the other of said cathode to anode paths to ground, said automatic gain control terminals being connected to an adjustable tap on said resistor.

4. A radio receiving system comprising a plurality of constituent receivers each including a signal detecting means and an automatic gain control circuit, each of said receivers havingterminals, a terminal connected to said detecting means to receive the output thereof anda terminal connected to said automatic gain control circuit, a combining circuit having an input and an output, means for coupling all of said detecting means terminals to said combining circuit input and means for coupling all of said automatic gain control circuit terminals to said combining circuit output, said combining circuit including a thermionic discharge tube having a plurality of cathode to anode discharge paths CHARLES PERCY BEANLAND.

REFERENCES CITED The following references are of record in the file of this patent:

UNITED STATES PATENTS Name Date Moore Mar. 15, 1932 Crosby Dec. 12, 1944 Number 

